Over the years, there has been developed a substantial body of patent and other literature directed to the formation and properties of poly(aryl ethers) (hereinafter called "PAE"). A broad range of PAE's was achieved by Johnson et al., Journal of Polymer Science, A-1, vol. 5, 1967, pp. 2415-2427, Johnson et al., U.S. Pat. Nos. 4,108,837 and 4,175,175. Johnson et al. show that a very broad range of PAE's can be formed by the nucleophilic aromatic substitution (condensation) reaction of an activated aromatic dihalide and an aromatic diol. By this method, Johnson et al. created a host of new PAE's including a broad class of poly(aryl ether ketones), hereinafter called "PAEK's".
In recent years, there has developed a growing interest in PAEKs as evidenced by Dahl, U.S. Pat. Nos. 3,953,400; Dahl et al., 3,956,240; Dahl, 4,247,682; Rose et al., 4,320,224; Maresca, 4,339,568; Attwood et al., Polymer, 1981, vol. 22, August, pp. 1096-1103; Blundell et al., Polymer, 1983 vol. 24, August, pp. 953-958, Attwood et al., Polymer Preprints, 20, no. 1, April 1979, pp. 191-194; and Rueda et al., Polymer Communications, 1983, vol. 24, September, pp. 258-260. In 1978, Imperial Chemical Industries PLC (ICI) commercialized a PAEK under the trademark Victrex PEEK. As PAEK is the acronym of poly(aryl ether ketone), PEEK is the acronym of poly(ether ether ketone) in which the phenylene units in the structure are assumed.
Thus PAEKs are well known; they can be synthesized from a variety of starting materials; and they can be made with different melting temperatures and molecular weights. Most of the PAEKs are crystalline and at sufficiently high molecular weights they are tough, i.e., they exhibit high values (i50 ft-lbs/in.sup.3) in the tensile impact test (ASTM D-1822). Thy have potential for a wide variety of uses, and their favorable properties class them with the best of the engineering polymers.
Some PAEK's may be produced by the Friedel-Crafts catalyzed reaction of aromatic diacylhalides with unsubstituted aromatic compounds such as diphenyl ether as described in, for example, U.S. Pat. No. 3.065,204. These processes are generally inexpensive processes; however, the polymers produced by these processes tend to be brittle and thermally unstable. In contrast PAEK's made by nucleophilic aromatic substitution reactions are tough crystalline polymers. Nucleophilic aromatic substitution reactions for producing PAEK s are described in the following references:
Canadian Pat. No. 847963 describes a process for preparing polyarylene polyethers. The process comprises contacting equimolar amounts of a dihydric phenol and a dihalobenzenoid compound and at least one mole of an alkali metal carbonate per mole of dihydric phenol. The dihydric phenol is in situ reacted with the alkali metal carbonate to form the alkali metal salt thereof and the formed salt reacts with the dihalobenzenoid compound to form the polyarylene polyether in the usual fashion.
U.S. Pat. No. 4,176,222 describes the preparation of aromatic polyethers containing SO.sub.2 and/or CO linkages by a nucleophilic reaction utilizing a mixture of sodium carbonate or bicarbonate and a second alkali metal carbonate or bicarbonate. The alkali metal of the second alkali metal carbonate or bicarbonate has a higher atomic numbe than that of sodium. The second alkali metal carbonate or bicarbonate is used in amounts such that there are 0.001 to 0.2 gram atoms of the alkali of higher atomic number per gram atom of sodium. The process is stated to take place faster when the combination of sodium carbonate or bicarbonate and the second alkali metal carbonate or bicarbonate are used. Also the products are stated to be of high molecular weight using such a combination.
U.S. Pat. No. 4,320,224 also describes the production of aromatic polyetherketones in the presence of an alkali metal carbonate or bicarbonate in an amount providing at least 2 gram atoms of alkali metal per mole of starting bisphenol. The patent states that the sole use of sodium carbonate and/or bicarbonate is excluded.
U.S. Pat. No. 3,941,748 describes the use of alkali metal fluoride for preparing polyarylethers. The process requires that sufficient fluoride be present so that the total fluoride available (including that from any fluoroaryl monomers) be at least twice the number of phenol (--OH) groups. The examples show it to be, in general, a slow process.
U.S. Pat. No. 4,169,178 refers to the British counterpart of U.S. Pat. No. 3,941,748, i.e., British Pat. No. 1,348,630. The patent states that the amount of alkali metal carbonate required may be reduced in the preparation of aromatic polyethers by employing fluorophenols or difluorobenzenoid compounds as part or all of the halogen containing reactants. The patent states that the process gives faster reactions and higher molecular weights and less colored polymers than a process using potassium fluoride in place of potassium carbonate.
U.S. patent application Ser. No. 713,845 filed in the name of D. R. Kelsey on Mar. 20, 1985 titled An Improved Process For Preparing Poly(Aryl Ether Ketones), and assigned to the same assignee as this application, described an improved process for preparing poly(aryl ether ketone)s by the reaction of a mixture of at least one bisphenol and at least one dihalobenzenoid compound, or of a halophenol, in which the improvement involves providing to the reaction a combination of sodium carbonate and/or bicarbonate and an alkali metal halide selected from potassium, rubidium or cesium fluoride or chloride, or combinations thereof.
Poly(aryl ethers) prepared by nucleophilic displacement polycondensation may contain both phenate and halo aromatic end groups, e.g., ##STR1## wherein X is a displaceable group such as halogen or nitro, M is the cation of the base used (e.g., Na.sup.+, K.sup.+, etc.) and Ar (Ar') is an aromatic species. In the prior art, it has been customary to add a terminating agent, also referred to as an end-capping agent or end-stopper, at the end of the polymerization to react with the phenate end groups, e.g., EQU Polymer O--Ar'--O.sup.- M.sup.+ +RX.fwdarw.Polymer OAr'--OR
For example, U.S. Pat. No. 4,108,837 illustrates in Examples the use of methyl chloride as a terminating agent; U.S. Pat. No. 4,169,178 illustrates the use of dichlorodiphenylsulfone; and U.S. Pat. No. 4,320,224 illustrates the use of 4,4'-difluorobenzophenone as terminating agents.
The use of an end capping reagent can be useful for controlling the molecular weight of the polymer. However, more importantly, the presence of phenate or phenolic end groups in the polymer can lead to thermal instability. Converting these end groups to ether groups by use of an end capping reagent results in generally improved thermal stability.
To assure that end capping is complete, an excess of end-capping reagent would be desirable, once the desired polymer molecular weight has been achieved, to assure that all of the residual phenate groups can react with the terminating reagent.
However, use of excess capping reagent can often lead to a significant decrease in molecular weight. This is known in the art; for example, U.S. Pat. No. 4,169,178 discloses that "end stopping may lead to some reduction in the polymer molecular weight." This patent illustrates in Examples 4, 6, and 7, for example, reductions in reduced viscosity of 0.11 to 0.29 within 5 to 10 minutes at 320.degree. C.-330.degree. C. after addition of a small amount of dichlorodiphenyl sulfone as the end-capping reagent.
This phenomenon has been confirmed in this application in Example E, which shows that addition of only 2 mole % of a difluorodiketone, i.e., 1,4-bis(4-fluorobenzoyl)benzene as end-capping agent results in a decrease in molecular weight from a reduced viscosity of 1.37 dl/gm to a reduced viscosity of 0.98 dl/gm within 1 hour at a temperature of 300.degree. C.
Attwood, et al. [Polymer, 18, 359 (1977)], have discussed the problem of terminating polysulfones prepared from fluorophenyl-sulphonyl phenoxides with methyl chloride due to depolymerization in the presence of potassium fluoride, which they depicted as the following: ##STR2## They suggested two methods to control the depolymerization during polymer termination: (1) cool the reaction to "freeze" the equilibration by potassium fluoride before termination, or (2) polymerize beyond the desired molecular weight, isolate the polymer, and then degrade the polymer in dimethyl sulfoxide with sodium methoxide to the desired molecular weight and terminate with methylene chloride.
Neither of these methods can be effective for crystalline poly(aryl ethers), especially poly(aryl ether ketones), since cooling the reaction mixture in such cases would lead to crystallization of the polymer and an intractable reaction mixture and these polymers. are generally insoluble in solvents such as dimethyl sulfoxide. Furthermore, the second method given by Attwood, et al., would be impractical and expensive on a commercial scale even if it were remotely feasible to perform. Attwood, et al. [British Polymer Journal, 4, 391 (1972)] also showed that polysulfones are cleaved at the ether linkage by fluoride ion, i.e., addition of potassium fluoride to a polysulfone resulted in re-equilibration to a lower molecular weight. With excess difluorophenyl sulfone also present, extensive depolymerization took place.
Poly(aryl ether ketones) also undergo molecular weight reduction in the presence of, for example, potassium fluoride and end-capping reagent.